fix gradle compliation (#925)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/925

Gradle is failing to compile yoga for two reasons:
1. Ever since `YogaNodeJNIPhantomRefs` was introduced which uses `DestructorThread.Destructor` from fbjni which was the first direct Java dependency from yoga java to fbjni java code.

2. Adding a missing gradle endpoint for `testutil` since it is now required for yoga unit-tests

Reviewed By: SidharthGuglani

Differential Revision: D17274226

fbshipit-source-id: 3df9648321162d34f81fd3675ca1474e8a1c6d3a

testutil/BUCK

@@ -1,10 +1,10 @@
-load("//tools/build_defs/oss:yoga_defs.bzl", "ANDROID", "FBJNI_TARGET", "LIBRARY_COMPILER_FLAGS", "SOLOADER_TARGET", "yoga_cxx_library", "yoga_dep", "yoga_java_library")
+load("//tools/build_defs/oss:yoga_defs.bzl", "ANDROID", "FBJNI_TARGET", "LIBRARY_COMPILER_FLAGS", "SOLOADER_TARGET", "subdir_glob", "yoga_cxx_library", "yoga_dep", "yoga_java_library")
 
 yoga_cxx_library(
     name = "testutil",
-    srcs = ["testutil.cpp"],
-    header_namespace = "yoga/testutil",
-    exported_headers = ["testutil.h"],
+    srcs = ["src/main/cpp/testutil/testutil.cpp"],
+    header_namespace = "",
+    exported_headers = subdir_glob([("src/main/cpp/include", "yoga/testutil/testutil.h")]),
     compiler_flags = LIBRARY_COMPILER_FLAGS,
     soname = "libyoga_testutil.$(ext)",
     visibility = ["PUBLIC"],
@@ -13,7 +13,7 @@ yoga_cxx_library(
 
 yoga_java_library(
     name = "java",
-    srcs = ["TestUtil.java"],
+    srcs = ["src/main/java/com/facebook/yoga/TestUtil.java"],
     source = "1.7",
     target = "1.7",
     visibility = ["PUBLIC"],
@@ -25,7 +25,7 @@ yoga_java_library(
 
 yoga_cxx_library(
     name = "jni",
-    srcs = ["jni.cpp"],
+    srcs = ["src/main/cpp/jni/jni.cpp"],
     allow_jni_merging = False,
     compiler_flags = LIBRARY_COMPILER_FLAGS,
     platforms = ANDROID,